1. Field of the Invention
The present invention pertains to a roller for a printer comprising an outer tube and positioned therein at least one inner tube. The outer tube extends in an axial direction from a first end to a second end and the inner tube extends substantially parallel to the outer tube, defining an inter tubular space between the outer and the inner tube and an intra tubular space within the inner tube.
The present invention also pertains to a printing system including such a roller and a method of cooling the surface of such a roller.
2. Description of Background Art
Such rollers are commonly applied in, e.g. electrophotographic printers. Rollers of this type are, e.g. used as image-bearing rollers or as cooling rollers. These are rollers that absorb heat in their operation and that require cooling of their surface. The cooling is usually done by blowing or sucking air through the interior of the roller with a fan.
Image-bearing rollers are, e.g. rollers that are covered with a photoconductive layer or with an electrode pattern. This enables the formation of an electrostatic image on the surface of the image-bearing roller. In a subsequent step, a layer of toner particles is developed onto the electrostatic image on the image-bearing roller. This toner image is subsequently transferred to the receiving substrate and fused with the receiving substrate.
During the operation of the printer, the surface temperature of the image-bearing roller tends to increase. If the surface temperature rises too high, the toner particles will fuse and stick to the surface of the image-bearing roller resulting in print artifacts. Therefore, the surface of the image-bearing roller requires cooling by, e.g. blowing air through the roller.
Rollers according to the background art are also used as cooling rollers. When such a roller is rotatably contacted with a substrate it will drain heat from that substrate thus cooling the substrate. The heat taken up by the cooling roller is then discharged with the air flow that passes through the roller. Optionally, it is also possible to discharge the heat with a flow of a liquid cooling agent that runs through the roller.
The disadvantage of the rollers according to the background art is that a temperature gradient is formed in an axial direction along the surface. This is because the cold air that is blown into the inter tubular space of the roller immediately exchanges heat with the surface of the roller. Thus, when progressing through the roller, the air flow temperature increases. This reduces the temperature difference between the air flow and the surface of the roller. This subsequently leads to a reduced cooling capacity of the air flow near the end of the roller which results in a temperature gradient over the roller. Because of this temperature gradient, the air flow must be sufficiently high in order to reach a specified temperature at the end to the roller. This leads to a relatively inefficient cooling system.